The possibility that extracellular dextranase contributes to the structural complexity of the adherent and insoluble glucan synthesized from sucrose by cariogenic streptococci is under investigation. For this project, a set of independent dextranase-deficient mutants has been isolated from Streptococcus mutans 6715-13. These mutants are being compared to their parent with respect to sucrose-mediated adherence to smooth surfaces, and the synthesis of soluble and insoluble glucans. The possible role of plasmids in the physiology and ecology of oral streptococci is being studied also. Currently under investigation is a tetracycine resistance trait from S. mutans. This trait is transferable to certain other streptococci via a conjugation-like mechanism, and a small plasmid has been identified in one of the recipients that had received the tetracycline resistance trait.